use $() instead of backtiks for command substitution, as it gives a more consistent behavior.

See https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html#tag_23_02_06_03 for more details

Author: baldurmen

manifests/backup/xtrabackup.pp

@@ -63,7 +63,7 @@
 
   $daily_cron_data = ($incremental_backups) ? {
     true  => {
-      'directories' => "--incremental-basedir=${backupdir} --target-dir=${backupdir}/`date +%F_%H-%M-%S`",
+      'directories' => "--incremental-basedir=${backupdir} --target-dir=${backupdir}/$(date +%F_%H-%M-%S)",
       'weekday'     => '1-6',
     },
     false => {